texts: Planetary tails: How many have we observed yet?

texts:
Just recently I learned that Mercury has a sodium tail and it is actually well studied since long:

As a result, the planet has the appearance of a comet, with a tail that's been observed streaming nearly 3.5 million kilometres away from the planet.

This made me wonder about exoplanets with tails, like WASP-69b. How many (exo)planets are known to have a tail?
References

Why would a planet form a cometlike tail under conditions of weaker rather than stronger solar wind?


texts: Do the gases in the Earth's atmosphere affect the color of a lunar eclipse?

texts:
As the sun's rays pass through the Earth's atmosphere only the red light gets through. Is this the result of specific gases in the Earth's atmosphere filtering the red light?  Does all of the nitrogen and oxygen affect the sunlight shining through it?

Let's say the Earth (or just about any earth-like planet) has an atmosphere made mostly of green chlorine. When the sun shines through the chlorine atmosphere and hits the moon during a lunar eclipse, would the moon appear green? Would different gases result in the moon becoming different colors?


texts: What happens to Europa's (or another ice moon's) water if we drilled a hole through the ice crust down to the ocean?

texts:
Suppose we drilled a 1 ft (30 cm) diameter hole through Europa's ice crust. As Europa doesn't have an atmosphere, the water would obviously either sublime (turn to vapor) or instantly freeze once a hole is drilled through, but how exactly would that be going on?
In the case of sublimation, the ocean won't sublime all at once, right? How fast would the sublimation be going on, how large of a volume of water would turn to vapor in a realistic time frame, or so?
In case of freezing, what would it look like if it froze instantly? Even before it froze, it would have to be liquid while exposed to the vacuum of space once the hole is drilled, which in turn would be impossible, or wouldn't it?


texts: Can Space-Time Itself Have Energy Qualities Like Momentum?

texts:
Hypothetically, if space could be moved or scaled, what would happen to everything inside?

I'd like to know if an element of momentum could be transferred to objects by contorting space-time.

Other than gravity, what effects does space-time contortion have on mass?


texts: Radioactive decay is the main source of the earth's interior heat: fact or theory?

texts: It's believed the main reason that the interior of the Earth hasn't cooled down in 4 billion years is because of the ongoing decay of radioactive elements that keeps adding more heat than is lost to the various cooling processes. Is this a proven fact or are there other possibilities?


texts: Why do stars twinkle but the Sun doesn't (I'm asking this because the Sun is also a star)

texts:
My friend asked me

  "Sun is also a star then why doesn't it twinkle like other stars"

I brought this question here so that I have (and have more) infomation on this topic.


texts: What should the mass of a planet be in-order for its escape velocity to be near the speed of light?

texts: What should the mass of a planet be in-order for its escape velocity to be the speed of light?  Is it even possible? What will it look like from an outside viewer? Will it even be visible in the human eye spectrum?


texts: Calculating Angle Between Two Planets In Heliocentric Orbit

texts:
My goal is to calculate the retrograde of Mercury. What I've been working from is the book, Practical Astronomy With Your Calculator 3rd edition. I've made some progress, but I seem to be stuck with how to get the right answer. Hopefully my data to work with is right. Here is a sample:
Sat Feb 20 03:52:00 2021
Direct:
Mercury: 160
Earth  : 77
Diff   : 83 : 237
Tue Jun 22 00:00:00 2021
Direct:
Mercury: 358
Earth  : 199
Diff   : 159 : 557
Mon Oct 18 00:00:00 2021
Direct:
Mercury: 124
Earth  : 314
Diff   : 190 : 438

All numbers are in degrees, based upon the main calculations from page 108. The calculations only cover part of the whole thing. Mostly to the bottom of page 108 #11. I then took the decimal part of the numbers I was getting for Vp and Ve, and converted that into degrees with a look up table. Also, I modified the formula in #2 to be Mercury's orbit period. Hoping to get more accurate data.
My question is: Can the angle between the two planets be calculated? I know the distance each planet is from the sun, but how can I get the angle between the two planets for the dates I've shown? I'm new to math like this, so forgive what I'm not aware of here.
Thank you!
See photo for formula used:


texts: How can a planet have a 90° inclination?

texts:
Planetary systems as we understand it exist from a disk of mass when the parent star is young.  That's why all our planets are in the same plane, or close to it.  See also Why is the solar system often shown as a 2D plane?,  Inclination of planets, and answers there.

Yet the newly announced Kepler-452b apparently has an inclination of close to 90° (89.806+0.134−0.049°).  Do we have any model of solar system formation that explains how this can form?


texts: Can the next possible ice age be projected based upon the Milankovitch cycle?

texts:
The Milankovitch cycle

  describes the collective effects of changes in the Earth's movements upon its climate[.]

By this theory, the Earth is now experiencing an interglacial.

By the theory, when will the interglacial end and the next ice age begin?


texts: Dark matter hypothesis and visible light

texts:
Dark matter is hypothesized as the mass based on gravitational observations is much higher than that observed via measuring how bright a galaxy is.

Why could it not be that multiple stars in the distant galaxy are in a straight line, blocking one another from view and so the brightness from the hidden stars can't be measured? Similar to how during a solar eclipse, the sun is not visible behind the moon? Granted the moon is much closer than the sun and blocks out most of the sun, but cumulatively the brightness from multiple stars in the line of sight would not add up.


texts: Are telescope eyepieces ever made with a diopter adjustment (similar to DSLRs)?

texts: I am learning about eyepieces, and "eye relief" and what sorts of eyepieces an amateur may want for their purposes, and was wondering if there are eyepieces with diopter adjustments, or if, due to the optical systems in reflecting and refracting telescopes, diopter adjustment like those in a DSLR viewfinder are never found in the designs of eyepieces.


texts: How many members of the IAU typically attend votes?

texts:
One of the talking points of people how think that the definition of a planet should include Pluto is that during the 2006 vote on the definition of a planet, only a small percentage of the members of the IAU actually voted (183 for, 186 against. 13116 total members), thus making the results of the vote not representative of a consensus among the astronomical community.

Where the number of members who voted that motion uncharacteristically low, compared to most votes taken by the IAU? Does this low number of voters indicate that this decision is not representative of what astronomers working on this issue think?


texts: How complicated is the heating of meteors?

texts:
When any gas, including our atmosphere, is compressed, it's temperature rises.
When a meteor is falling through the atmosphere, it is compressing the air below it.
Because this makes the air hotter than the meteor, heat moves from the air to the meteor.

Also, some amount of oxidation (burning) might also take place.

What I would like to know, is it really that simple?

Alternatively, what else causes meteors to heat up?

I've heard people say "air friction," which sounds to me like nonsense, but I am not a rocket scientist, so what do I know?  If "air friction" is real I want to know how it works!

Also, I'm fairly certain that heating of air due to turbulence will only affect the air which the meteor has already moved through... not the meteor itself.  If I'm wrong, I want to know!


texts:
As Wikipedia says,

  In celestial mechanics, the Kozai mechanism, or the Lidov–Kozai mechanism, is a perturbation of the orbit of a satellite by the gravity of another body orbiting farther out, causing libration (oscillation about a constant value) of the orbit's argument of pericenter. As the orbit librates, there is a periodic exchange between its inclination and its eccentricity.

My questions are:

Question A
Which is the least massive object? The tertiary object, which is the furthest object, or the satellite in the inner binary? It seems it is not necessary that the tertiary object be the least massive one, which violates what Wikipedia says.

Question B
How does the three-body system evolve?

  There is a periodic exchange between its inclination and its eccentricity.

Whose inclination and whose eccentricity? Please specify them using m0, m1 or m2 in the figure below.

The orbit of the inner binary should become and more circular. Can it become circular, eccentric, circular, eccentric?

Question C
The inner binary will lose energy during the whole process, right?


texts: Problem regarding the absorption lines of the sun

texts:
Some of the wavelengths of light that are emitted from the sun will be absorbed by atoms in the outer layer of the sun and also the atmosphere of the sun, and we see this as absorption lines in the spectrum. Now, this absorbed radiation will indeed be re-emitted again, so one might think that these emission lines should "cancel out" the absorption lines. The usual explanation for why this doesn't happen is that the re-emitted light is radiated in all directions, not just towards us, meaning that to us these wavelengths will be much fainter than the other wavelengths.
But the problem I have is that this happens all around the sun (since the atmosphere is completely surrounding it), and intuitively it seems then that all of this re-emitted light should combine such that far away it would appear that the sun is radiating these wavelengths just as it is radiating all the other wavelengths. And if that is true, then we shouldn't see absorption lines in the spectrum. So what is it that I am missing?


texts: Is scattering efficiency of dust related to albedo?

texts: I know that the scattering cross-sections of dust in comets depend on the scattering efficiency. A higher scattering efficiency leads to an increase in brightness. Therefore, does it mean that this will also increase the albedo or these quantities are not related at all?


texts: The boundary of a black hole is said to be surrounded by event horizon - the point of no return! What is its significance in terms of general relativity?


texts:
This is a basic question, but I may as well ask it. I had always thought that the core of a main-sequence star is defined as the part hot enough for nuclear fusion. Some dictionaries seem to agree with this.

However, many books say that protostars and pre-main-sequence stars also have cores, though they are not undergoing hydrogen fusion.

So what exactly is the definition of a stellar core? If it doesn't necessarily have to be hot enough for fusion, what separates it from the rest of the star?


texts: What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?

texts: I assume that about 99.9% of the sun-rays that do not fall on any planet or any other celestial body keep on traveling farther and farther unto infinity. Apparently such rays get lost. Keeping in mind the colossal energy Sun has produced since 4.5 billion years I am somehow reluctant to  reconcile myself to the idea that Nature would have allowed wastage of so much energy produced by the Sun. Nonetheless I want to get enlightened whether it got really lost or got utilized. If it got utilized I want to know how it may have got utilized at all and whether any sustainable evidence is available in support of any such finding?


texts: Synthesising types of galaxies using various stellar spectra

texts: I have asked this on Physics Stack Exchange but Astronomy is probably more appropriate. I have been given the task of synthesising an elliptical galaxy, a starburst galaxy and a spiral galaxy (considering the arms and the bulge separately and adding them) using stellar spectra which I have classified. I need to add different weightings of five types of stars to produce a normalised spectrum of each of these galaxies. I have spectra for giants, main sequence stars and sub-giants with varying stellar types (O, B, A, F, G, K, M). I know that Spiral arms and the starburst are going to be primarily young stars, while the spiral bulge and the elliptical will be of older stars, but I have no idea which types or luminosity classes of stars I would use and their weightings in each. Can anyone offer any information or resources where I would find good information on adding different types of star to 'create' a galaxy?


texts:
In this publication from 1981, was shown that Neptune is raining diamonds:

  Many of the current models of Uranus and Neptune postulate a three-layer structure, consisting of an inner rocky core, a middle ‘ice’ layer of fluid, $\rm H_2\rm O$, $\rm{CH}_4$, $\rm{NH}_3$ and an outer hydrogen–helium layer of solar composition. The estimated pressures and temperatures of the ice layer range from about 6Mbar and 7,000K at the inner core-ice boundary to $\approx$ 0.2 Mbar and 2,200K at the outer ice/hydrogen–helium boundary. I point out here, that shockwave experiments on these liquids, as well as theoretical studies, imply that the $\rm H_2\rm O$ and $\rm{NH}_3$ in the ice layer are almost totally ionized, and the $\rm{CH}_4$ has been pyrolysed to carbon, possibly in the metallic or diamond form.

Question: In the decades since this work was published in 1981 have these predictions been addressed further, or even proven or disproven?

If this turns out to be true, would these diamonds have different physical properties than those on Earth because of the different formation mechanism?


texts: How close are we to having the technology to measure planetary obliquity for exoplanets?

texts:
As far as I can tell, we do not yet have the precision to even put reasonable bounds on an exoplanets obliquity, but wikipedia seems to indicate that this may be possible in the "near future." It seems like this would have to be accomplished by direct imaging, either by directly observing rotational flattening of an exoplanets, or by looking for moons and assuming that the planet is tidally locked to the same plane as its satellite.

How close would you estimate we are to this kind of precision? Are there other approaches to measuring planetary obliquity?

Obviously, I'm not expecting a definite answer. Just wondering if anyone knows of any research in this area or has any thoughts about it.


texts: Trajectory: What would happen if the sun disappeared one day?

texts:
So, let's just assume, to no aspect explainable to humans, the sun just magically popped out of existence on January 1st next year (2022), that'll never happen, this is just a scenario to explain my question. If the sun disappeared, regardless of life on Earth, where would the Earth float off to? If it would come close to a gas giant, then a gravity assist would affect the Earth's path through space. Where would it go?
In an answer, I want a feasibly explained way to calculate where Earth would go, not giving much thought to Gravity assists, since I got their calculations from this question, the first answer, and the answer in the link embedded in it.
Also, in the comments section, I've seen comments claiming that my question is a possible duplicate of others. One other addresses what would happen here on Earth, while the other one is about how long it would take for us to stop orbiting the sun after its sudden disappearance. In contrast, I'm wondering about where the Earth would float off to, and where it would go.
Now, this question can seemingly be applied to any celestial object, whether the sun is there or not, I want to figure out trajectory in space. I want to know about trajectory, and how it affects the motion of celestial bodies.
Assuming this can be answered theoretically by the use of equations and mathematics, thanks in advance!


texts: Can the Milky Way be seen with the naked eye? Does this apply to any galaxy? If yes, then how and when?

texts: I have seen different pictures in a different community to showcasing the Milky Way. I can never tell whether it's edited or it's the real picture. Actually, I can never see any galaxy as such by with my naked eye. But can the Milky Way be seen with the naked eye? If yes, then I would really like to know when and how this is possible.


texts: Can one build a distributed radio telescope?

texts: I understand some radio telescopes are built as arrays of receivers. Could one build an array from a heterogeneous set of receivers in scattered locations? Suppose a large number of persons each operate a receiver, and data is gathered together; can it function as an array? Asking for a friend.


texts: How would you relate the respective solar gravitational pulls of two planets?

texts:
I was asked this question:

  How much weaker is the gravitational pull of the Sun on Neptune at 30 AU, than it is on Earth at 1 AU?

How would I even begin to determine this?


texts: If Earth had no atmosphere, how many people would be killed by meteors every year?

texts: Suppose those people engage in similar activity, walking on surface etc.


texts: When I read some papers about MHD dynamo theory, there is always a $\tau$ that means convection overturning time. What does convection overturn mean?


texts:
From Question #6 of USAAAO First Round 2018

  (1 point) For the following problem find the range in which the answer lies: on the day of summer solstice, on which geographic latitude is the sun culminating at the angle of +72° 50' north of the equator?

  A. 0° − 15°
  B. 15° − 30°
  C. 30° − 45°
  D. 45° − 60°
  E. 60° − 75°

I have two answers: 41° and 6°, but only one is accepted. No solutions are provided for 2018 and it is an objective question.


texts: Are there any hot jupiters orbiting red dwarfs?

texts: Do we know of any hot jupiters that could be orbiting a red dwarf (or, more probably, orbiting a barycenter between the two)? Is this scenario even physically possible?


texts: How to calculate the new orbit after a instantaneous change in a well defined initial one?

texts: Say one has a simple two body system (and one body is much more massive than the other, for example a star, planet system) where all the quantities about it are know, that is the eccentricity, masses, perihelion, etc. Now, at some point in the orbit defined by the polar coordinates at that point, there is a instantaneous change in velocity. Now, the question is what will be the new orbit of the object around the other body? What are all the components of that orbit such as eccentricity, perihelion. Can the system even be solved exactly or only analytically?


texts:
Type 1a supernovae are used as standard candles. Are there other high energy cosmic events which can be used as standard candles. For example, collapse of neutron star into a black hole is also similar to type 1a.

In a galaxy, there are far more white dwarfs(candidates of type 1a) compared to neutron stars(I read somewhere that our galaxy contains around 200 million of them). Also, the energy released in neutron star collapse is not in visible spectrum(I don't think so that is the criteria for "standard candles"). Are these the reasons that neutron star collapse is not qualified as another type of standard candle?


texts: Number of obscured AGN compared to unobscured AGN

texts:
Urry and Padovani 1995 proposed a unified model for Active Galactic Nuclei, which has since been recognised as a good model for AGN. If AGN are randomly oriented, then I'd expect there to be more obscured AGN than unobscured, because there would be more orientations that would make us look through the sides, than along the axis:

Is this the case? In other words, how many obscured-type AGNs (Seyfert 1 or 2 Galaxies, radio galaxies, radio-quiet quasars, NLRs) are there, compared to unobscured AGN (BLRs, blazars, radio-loud quasars)?


texts: Which star has the lowest absolute magnitude?

texts: I have seen many lists of stars with the most luminosity, mass, and temperature, but I have never seen one that is about absolute magnitude. So I'm wondering, which star has the lowest absolute magnitude (in other words, which star is the brightest when a viewer is 10 pc away)?


texts: How reliable is it to use globular cluster lumniosity function as a distance indicator?

texts:
I have seen many research suggesting that GCLF can be used as a secondary distance indicator for extragalactic objects. However, this method seems to be only reliable when the GCs in use come from say, a single galaxy, and it can be used as a secondary distance indicator for the home galaxy.
My question right now is that I have large all sky survey data with extracted potential GCs candidates ranging from 1 to 20 Mpc. These can be considered as "rogue" GCs that do not necessarily belong to any galaxy. Can the GCLF be used to obtain at least some very crude estimates of the distance of individual GC? What I mean by that is we will obtain some probability distribution of the distance through GCLF and how reliable is the distance information provided by the previously obtained distribution? Thank you!


texts: Predicting Temperature Variation on Planets with High Eccentricity or Long Diurnal Periods

texts:
Whew! That title was a mouth-full, but accurate I hope. What I'm trying to figure out is a model for calculating the approximate temperature variation for a generally earth-like planet (similar atmosphere, large oceans, etc.) under two concurrent conditions:

High Eccentricity: 0.1, 0.2, 0.3 etc.
Long Diurnal Periods: 72 hours - 960 hours (the later could reflect a planet in a 2:1 orbital resonance around a M Star).

(Assume Obliquity = 0 so as to simplify things)

I know conditions like the mass of the atmosphere and the size of the oceans play a key role in the retention and redistribution of heat. However I've been unable to locate any research papers or explicit models that would help. It's relatively straightforward to calculate real temperature (effective temperature modified for greenhouse effect) for both periapsis and apoapsis, however I've had no luck in finding resources for figuring out how much of this temperature variation would be mitigated by retention and redistribution. Same with long nights and long days.

If a specific example would help, let's consider a planet with the following characteristics:

30-day orbit
15-day (720 hour) rotation (2:1 orbital resonance)
30-day solar day (sunrise to sunrise)
0 obliquity
0.25 eccentricity
Earth-like in other respects

Calculations or even simply links to applicable research papers would be immensely helpful. Thanks!


texts: Calculating distance from center of mass of two stars in a binary system

texts:
I am confused on how to calculate the distances for each star in a binary system to their centre of mass. I am trying to solve it from a book I am reading which shows the solution but I do not understand the solution.
So the info I am given is:
A system is located at a distance D (in parsecs). The two stars orbit around their centre of mass. Star A has an angular separation of a (in arcsecs) and star B has an angular separation of b (arcsecs).
So now I am trying to find the physical separation of the stars to their centre of mass.
The book's solution (once converting to correct units) is:
Distance for star A = D tan(a)
Distance for star B = D tan(b)

I don't fully understand why they use tangent here because when I draw out a diagram of this situation i seem to need to use sine not tangent.
Here is how I drew it:

Why do they use tangent function and not the sine function? Have I drawn my diagram correctly?


texts: Is a supernova's core temperature absolute zero just before collapse?

texts: I thought a supernova's core temperature was absolute zero just before it collapsed, as it has run out of all nuclear and thermal energy, but I haven't been able to confirm this online anywhere and I was wondering if anyone can confirm this for me.


texts: What kills us in the event of two galaxies combining?

texts: I find the joining of galaxies interesting as the two eventually become ONE. On series I saw on a discovery channel stated we die.  Everyone dies. What is it that causes us to die when the galaxies combine? Is it something colliding with the Earth from the other galaxy such as a planet? Is it the drastic element changes on the Earth such as extreme temperatures or flooding, etc. Do we have any percent of surviving on Earth?


texts: Determine distance to Moon after diurnal parallax?

texts: So, I want to find the distance to the Moon/any body after performing the correction for diurnal parallax. Unfortunately, the resources I have do not cover how to do this. Is there an easy algorithm to adjust the distance to an object after switching to topocentric coordinates, assuming an ellipsoidal Earth?


texts: Is it possible to witness a star's death?

texts:
Given that the stars' distances to Earth are measured in light-years (for example, Sirius is 8.6 light-years away from Earth), what we are seeing as Sirius now is actually its state 8.6 years ago, right?

So it is possible that a star (maybe not Sirius, I don't know, it's just an example) somehow explodes and creates a supernova, and if this is the case, we will see this event 8.6 years later (I assume everything is right up to this point).

So my question is, is it possible for me while looking at the sky on a lucky day, suddenly see the explosion of a star that happened x years ago and be the first eye witness of this event? In other words, is there a technology on Earth (emphasis on "on Earth" here, the satellites or space shuttles do not count since they might be slightly closer to the star than the Earth is) that can see this before me?

My logic is that even the greatest telescope "sees" whatever light it receives. So since a telescope cannot increase the speed of light it receives, it shouldn't be more fast than me. And since light is the fastest way of transferring information, I assume that I am as possible as NASA to see such an event. Is there any way this assumption is wrong?


texts: applying nutation to ecliptical coordinates (apparent position of star)

texts:
I'm trying to calculate RA and DEC with nutation correction. The direct calculation in MEEUS Page 151 can't be used for stars close to celestial poles and I thought I'd turn RA/DEC into ecliptical longitude and latitude and then add delta psi to the longitude and transform back to RA/DEC. Unfortunately my calculations are wrong somewhere and I can't figure out where I made a mistake.
You can find my spreadsheet here: https://1drv.ms/f/s!AukrJ2RhCvoHh0w8MygI0qajeoXt


texts: Help identify a bright and round object photographed through a telescope

texts:
It was a brightest object in the sky. Attached is the picture taken on 25th January around 6pm in Riga / Latvia, towards the south direction:

Apologies for a quality of the picture, the telescope was inside the flat and the picture was taken through the window.

The object was visible for few hours while it was traveling from the south-east towards south-west. I observed this bright object previously on couple other days, it's the first time I pointed my tellescope in its direction.

View of the sky: https://imgur.com/iwRfmKa


texts: Orbital decay of the Earth's orbit and Earth's moving closer to the Sun

texts:
If we consider orbital decay of the Earth's orbit, then can we counter argue with the following reasons?

Due to tidal effects transferring small amounts of angular momentum from the Sun's spin to Earth's orbit, can we conclude that Earth's orbit is actually moving slightly further away from the Sun?
Can we say that the orbit is increasing in size because the sun loses millions of tons of mass each day, mostly to the ejection of particles called solar winds?


texts: It is said that in Blackhole 100% part of the mass is getting converted into energy. Then how come Blackhole is having mass ?


texts:
I need a bit of advice. I purchased a Orion xt8 and a lens kit with a 2x Barlow 6mm 20 mm eyepieces and every time I try pulling things into focus / magnification or focus goes out the window recently purchased a 5x Barlow to try to get the images bigger. But I’m starting to get a bit discouraged as the only thing I can see in the sky is the moon. All others. Clusters. Andromeda. Mars  I can not pull into focus to save my life.

I don’t know what I’m doing wrong. I see all these pictures of Andromeda from the same telescope and on mine I see dots. (Above picture is the most dots I could see near a cluster. But it’s not the cluster. I guess my question would be. How can I see objects in higher mag / detail. Andromeda is a dot like a star. So are all the planets.

And yes I know what to expect. I know things will look very blurry or out of focus. But only seeing star dots (when they are planets) concerns me.


texts: What determines whether or not photons can be absorbed by matter? Intuitively, the answer is that a charged particle can absorb photons (whether it's positively or negatively charged), and neutral particles can't. But light is often absorbed by atoms in bulk matter, increasing their thermal motion. The problem with this is that atoms are neutral, and so you wouldn't think that they could absorb light.


texts: What are the effects of using non-spherical lenses in refracting telescopes?

texts:
Non-spherical (or non-circular) mirrors for reflecting telescopes are common and discussed in many places...
But what about elliptical, parabolic or hyperbolic lenses?


texts: Are there stars in the first photo from space?

texts:
Wikipedia has this photo (see below) labelled "First photo from space" which was taken in 1946 from a U.S. launched German V-2 rocket. Approximately two thirds of the image is a section of the Earth showing some clouds and their shadows. The photo is very grainy so it's hard to see much more detail than this (I can't make out any land masses as all).

In the large black section occupying the top-left corner there are some very faint dots. Are these dirt on the lens, marks on the film, JPG artifacts or are they actually stars?


texts: How would a retrograde satellite experiencing tidal deceleration affect the rotation of the primary?

texts:
There are two common scenarios like this one, where an orbiting body orbits its primary slower than the primary rotates, resulting in the orbiting body moving away and the primary experiencing a slowdown in rotation. Whereas in the opposite, an orbiting body that orbits faster than the primary's rotation spirals in while the primary's rotation spins faster.
I know that a retrograde satellite will experience tidal deceleration and spiral in toward its primary body, but how will it affect the rotation of the primary?


texts: How do I determine the velocity of Pluto at aphelion and perihelion?

texts:
I am a college astronomy student and I have to find the velocity of Pluto at aphelion and perihelion. I have found the distance of perihelion to be $1.96\times10^9$ km. Aphelion has a distance of $3.27\times 10^9$ km.
It is given that Pluto's "minimum orbital velocity is 3.27 km/sec". Which I think means the velocity of Pluto at aphelion is 3.27 km/sec. But then how do I find the velocity at perihelion?


texts: So a couple days ago, my husband and I spotted a moving object in the sky just like a star. I know it wasn't a plane or a drone, and it was way up in the sky just a star. It just moved smoothly across the skies and than disappeared. I love to observe the sky so that was priceless for me and my husband.


texts: Detect sources near image edge with python photutils

texts:
As my question suggests, I 'm trying to use a python library photutils in order to detect sources from MUSE cube. MUSE (Multi Unit Spectroscopic Explorer) is an instrument which provides cube, i.e. an image for each wavelength within a certain range.

This is my code:

def extract_cat2(data, error, kernel, wcs, mask):
    bkg_estimator = MedianBackground()
    bkg = Background2D(data, (50, 50), filter_size=(3, 3), bkg_estimator=bkg_estimator, edge_method='pad', mask=mask )
    threshold = bkg.background + (3. * bkg.background_rms) + 2.*error
    #threshold = detect_threshold(data, nsigma=1.2.)
    #data = data - bkg.background
    segm = detect_sources(data, threshold, npixels=10, filter_kernel=kernel, connectivity = 8, mask=mask)
    segm_deblend = deblend_sources(data, segm, npixels=10, filter_kernel=kernel, nlevels=32, contrast=0.001, connectivity = 8)
    cat = source_properties(data, segm_deblend, wcs=wcs, filter_kernel=kernel, mask=mask)

Bacally, for each image, I estimate a threshold above which detect sources. As you can see, I add to the background also an error, provide by the instrument. The idea behind this is that threshold is higher when errors are larger.

In the image the result is shown overlapping the extracted sources to a MUSE frame (around 814 nm), as you can see, thinks work well far away from the edge of image. On the edge the number of detected sources increase. This is due to the noise: the detection algorithm is not able to disentangle noise from information, resulting in a large set of false positive detection.
How can I remove automatically such sources? Consider that I can not simply remove ALL sources within a certain separation from the edge, since among them there are some true detection. Thanks!


texts: Why can't we feel the Earth's revolution?

texts:
I googled it and checked a few Q&A and there's only things about "Earth's rotation". But why can't we feel the revolution?

They say we can't feel the rotation because the Earth spins at a constant speed. Okay, I get what happens for the rotation, but isn't it different when it comes to the revolution?

At night we feel the sum of speed of green and blue, whereas at day we should feel the sum of speed of green and minus blue, shouldn't we? In other words, shouldn't we feel the changes in velocity by times?


texts: If we had a hypothetical spacecraft, would it be possible to exit our galaxy, wait for some time and enter back into another section? Will this method be more efficient that a more traditional flight path?


texts: Will a Ball placed close to Sun fall into it?

texts: Like a ball falls on the earth due to gravity, if suppose we are able to place a ball close enough to the sun. Will the ball fall into the sun due to its gravity or will it be pushed away due to its energy?


texts: What's the first written record of the moon being tidally locked to the earth?

texts:
I couldn't find references as to who first noticed (wrote down) that the moon was tidally locked to the Earth. This, to me, doesn't seem obvious from first glance, and looks like something only found with cautious observations.

More specifically, I'd want to know when this first realized, from this question I gather that even acknowledging the moon as a moon took a long time, but the observation (or explanation of it) that it is tidally locked is missing from that.

Would be surprised if Aristarchus of Samos already noticed this!


texts: How do accretion disks around black holes evaporate via winds?

texts:
I'm curious as to how accretion disks around black holes evaporate. I've heard winds play a crucial role in this. But what winds specifically and how do they form? Is it a stellar wind of sorts? If so how effective would it be?
I've also heard radiation pressure causes these winds, but that shouldn't work unless the black hole is still in an X-ray binary. Any help is appreciated.


texts: Are all solutions of the 3-body problem restricted to 2 dimensions?

texts:
I am not a physicist.
Suppose there are two massive bodies orbiting each other. Their orbit will presumably define a plane.  As far as I know, the existing solutions to the 3-body problem are limited to a plane.
Has any work been done on 3-dimensional orbits? For example two bodies are orbiting one another and a third body enters the system at right angle to their plane?
Specifically (1) Are there any solutions even for special cases of this? (2) Would such 3-D systems inevitability decay into 2 dimensions?


texts: How were the orbits of planets first mapped out?

texts:
I'd like to know how the orbits of planets were first 'mapped out' and to understand the maths behind it. e.g. How do we know what position in space a planet will be at certain time so that spacecraft trips to planets could be planned etc.?

I'd also like to know the most primitive way that this could be done and if there is anyway this could be done using only maths and simple measuring tools assuming no previous knowledge about the planets positions.


texts:
I am trying to do exhaustive optical emission line analysis of some active galaxies using archival data.
What are some of the publically available data archives from where one could obtain optical emission line data? I am new to this, and so far I've found the HST MAST Archives and SDSS DR16.


texts: Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?

texts:
The Supernova 2006cm has a redshift of 0.0153 which translates into a recession speed of 4600 km/s.

It has a distance modulus of 34.71 which translates into a luminosity distance of 87 Mpc.

This gives a value of 53 km/s/Mpc for the Hubble constant.

Why doesn't this anomalous observation create sufficient doubt in the value of the Hubble constant?


texts: What proportion of planetary systems have been found with 'Hot Jupiters'

texts:
According to the NASA website "The strange attraction of Hot Jupiters", one of the main types of exoplanets that have been detected are Hot Jupiters, which are

  These are behemoth worlds that orbit close to their parent stars, blocking a fraction of the star’s light when it transits in front.

Planets that are from as large as Saturn through to far larger than Jupiter, orbiting in a matter of days very close to their parent star.  Something our solar system does not have.

What proportion of star systems have Hot Jupiters within their systems?  Is it a case that Hot-Jupiter-less systems such as our own are unusual?


texts: What is the accepted theory as to why Uranus' axis is tilted so severely?

texts:
The planet Uranus is another solar system anomaly, where according to the NASA profile has an axial tilt of 97.8 degrees, also considered to be retrograde.  This NASA summary "Uranus" suggests the current theory of a large planet-sized impact earlier in its history.

Does the planet-impact theory still hold true or have new accepted theories come to light?

Most of all, are there any results from any simulations available?

A note, this is posted as a separate question to my other question "What is the current accepted theory as to why Venus has a slow retrograde rotation?" as the axial tilt is significantly different.


texts: What liquids can be found in the void space?

texts:
Is there any material natural or otherwise a free floating liquid that can exist in space?

https://space.stackexchange.com/questions/32274/what-liquids-last-the-longest-in-space


texts: What are the equations for an orbit with time as parameter?

texts:
I am preparing a talk on the Equation of Time, and I want to produce an animation of the movement of the earth around the sun, in an exaggerated ellipse, to illustrate the speeding up and slowing down in different parts of the orbit. Ideally I would like to have x and y as functions of time, e.g x = f(t) and y = g(t). Accuracy is not the prime consideration, a reasonable approximation will do.

I will use a Processing sketch to produce the animation.

Can anyone please tell me what these equations are?


texts: Does supermoon's white light splits into seven colours

texts: I took a photo of SuperMoon 2016 and it was very shiny, the light around it showed seven colours. Was it my camera's effect or was it the moonlight's true colours.


texts: Why was the size of the solar system not defined by Mercury Transits?

texts:
The first measurements of the (absolute) size of the solar system was made using the Transit of Venus, an event that arguably will only happen twice in a lifetime.

Transits of Mercury occur far more often. Why have astronomers had to wait for Venus Transits to make historical measurements of the size of the solar system?


texts: I came across this page which provides (mostly extrapolated) speeds of both voyagers. Assuming they are fairly accurate, any reason why the speed of Voyager 2 (5-6 km/sec) is less than that of Voyager 1 (13 km/sec).


texts:
I would like to use a system of co-ordinates (x,y,z,t) based on a specific well known point. My original choice (the center of the universe in the big bang theory, Bigbang0), was wrong as the universe did not explode everything moved apart from everything else and is still doing so.
So I would like a reference position useful to an observer within at least 100,000 light years, and valid for 250,000 years. I will call it Bigref0 to remind me of my error.
From Bigref0 I would have a position - x y z.
The time value I would like to use as an origin is based on the following criteria.

The centers of the Sun and Earth are most closely aligned to the Bigref0.
The time point t0 should be the closest point within 256 tera (2 to the power 48) seconds or about 8 million years which provides a reasonable accuracy. I doubt we can do better than 1 part in 25,000 or +/- 2 to the power 15.

The questions are

When was/will be t0 ?
What is the distance (r0) to Bigref0 from the center of the Sun at time t0?
The x y z position of the Earth relative to the center of the Sun at time t0 ?
The accuracy/stability of the 5 values (t0,r0,x,y,z) ?

Example
The point in space time where the line through Earth and Sun is the closest to a line running from the Our Galactic center to the center of the local cluster.


texts: What is the difference between a neutron star and a white dwarf? I know that both are very dense even if they go through different phases.


texts: What happens to the information on the event horizons of two merging black holes?

texts:
What happens to the hairiness/information on the horizons of two black holes if they collide?

After Hawkin the information of the matter which has fallen into the blackhole is encoded on the surface of the event horizon. What happens to the information of both blackholes when the event horizons merge?


texts: Why does the moon sometimes appear giant and a orange red color near the horizon?

texts:
I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high above the horizon being generally further away than objects closer to the horizon.

But every once in a while, the moon looks absolutely huge and has a orange red color to it. Booth the size and color diminish as it moves further above the horizon. This does not seem to fit in with the regular perceived size changes that I already mentioned.

So what is the name of this giant orange red effect and what causes it?


texts: How many solar masses is the central black hole in the Whirlpool Galaxy?

texts: I am having trouble finding the mass of the central black hole in the Whirlpool Galaxy M51a/NGC5194, it is stated that its companion galaxy NGC5195 has a supermassive black hole at its centre that is 19 million solar masses but I can't find details on the Whirlpool Galaxy's central black hole, is its mass known?


texts: Generate East and North unit vectors tangent to a point on the celestial sphere, using vectors?

texts:
I am stuck and a little embarrassed.

I'm trying to implement this answer. I have a unit vector $w$ pointing in the direction of a radio source on the celestial sphere.

$u$ and $v$ are the two other, mutually orthogonal unit vectors that point east and north from that point, tangent to the sphere.

Without back-converting to R.A. and Dec or using trigonometry, is there a simple way to generate $u$ and $v$ vectorially?

Slide 38 here may or may not be helpful, I think my description is sufficient by itself.


texts: When was it first determined that the Sun is a star?

texts:
Just looking at the sky, it is not at all obvious that the Sun is a star: stars are fixed on the celestial sphere, they are point-like and not very bright, whereas the sun is a big (compared to a star) sphere that moves through the sky, making plenty of light. To know that they are actually the same kind of object, I guess you would first have to figure out that stars are much further out.
When was it first hypothesized that the Sun and the stars might have the same nature? What was the first element of observational evidence used to backup that idea?


texts: Birth and Evolution of Millisecond Pulsars

texts: How are millisecond pulsars formed, and what is the evolutionary track of a millisecond pulsar?


texts: How can I determine the location of an object for one observer given the location for another?

texts: I know an object exists at the location of the beam-pointing-center of a radio telescope. I know the elevation/azimuth of the beam pointing center, as well as it’s “location” in galactic coordinates. I want to determine at what elevation/azimuth I’d need to point the beam-pointing-center of radio telescope, on another point on earth, to also “point at” the object. For now, I’ll be doing this with pencil/paper, but it will eventually require an implementation in Rust.


texts: Matter and Antimatter Interaction in the early Universe

texts:
Well it is said that during the Big Bang, things were created in pairs: one matter and one anti-matter. I think its a part of the Big-Bang Theory.

It is also said that matter + anti-matter - Energy

Then shouldn't it be so that there would have been no matter or antimatter in existence now since all of them should have reacted to form pure Energy. I mean how were we created then?

And also where are all the antimatter gone now? Are they still reacting with us?

Thanks


texts: How much larger would a star have to be to cause thermonuclear reactions if it was made out of mostly rock like Earth, instead of gases?

texts:
I assume it would have to be considerably larger since rock isn't as flammable as gases are? But it's also more dense to begin with..

Do we know of any suns that are made like this?

Is it even possible to have a thermonuclear reaction with solid rock?


texts: Universe Sandbox 2 is the second installment of Universe Sandbox that is available on Steam. It is an educational simulation game based on astronomy and anything space, it ranges from supernova animations to climate and atmospheric simulations (and of course collisions) but do any of these features hold water? Do they truly resemble the dynamics of space?


texts: Could a Jovian or Saturnian moon keep its atmosphere if the system was within the habitable zone?

texts:
Currently the atmosphere of Titan is 1.5x thicker than Earth's atmosphere, but it's also much much colder. It's been said that an astronomical body can keep it's atmosphere if the escape velocity is more than six times the average speed of the molecules.

Does this mean if a moon like Titan was moved to the habitable zone and heated up to livable temperatures, then it's atmosphere would escape?

What is the minimum gravity necessary for a moon to hold onto an earth-like breathable atmosphere within the Habitable Zone?


texts: Celestron NexStar 130 SLT Computerized Telescope GoTo Not Accurate

texts:
I am trying to use a Celestron NexStar 130 SLT Computerized Telescope, but I am not able to use the GoTo function.

I do the three start alignment, it confirms matches,
I make sure the level is exactly level before and after,
I finally punch in a planet to slew to

...and once the telescope has slewed to the planet I see nothing in the eyepiece except pin point dots spread out.

Also, the words on the hand control are very hard to read because the letters are overlapping each other while the words are panning off the screen. I already tried factory resting which didn't work. The words are in English.

What would my next step be?

Example image, Source


texts: What would the tides on the Trappist-1 planets be like?

texts:
In the recent press conference about the planets orbiting around Trappist-1, one of the astronomers mentioned that the planets are close enough to each other that the tidal forces between planets are non-negligible. Supposing there were oceans on 1, 2 or all 3 of the planets in the habitable zone. What would the tides on these planets look like?

Because the dynamics of planet-planet interactions would be quite different from a planet-moon interaction, the tides would be far more complicated than a sinusoidal low-tide/high-tide at any given point on the planet. The abstract of the Nature paper on these planets states:

  The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers.

What effect would this have on the tides? How powerful would the tides be?


texts: How do we know the big bang expanded space and there wasn't a pre-existing volume for the universe to expand into?

texts:
Whenever we hear an explanation about the big bang, it is always phrased in such a way that it was an explosion which used some kind of pressure to expanded the universe out.

I wonder, however, would it be possible that our universe bubble started as a point that wrapped around the singularity and contained it.  Then, for some reason, this bubble started to expand, which caused the energy in the singularity to fill the newly created empty space.

Could it be that this bubble, which is now our universe, is still expanding, and the universe is still trying to fill the space, which is why we see dark energy?

Could we even know, or would either way look exactly the same to us?


texts: I just seen this in sky a line of stars probably satellites just wondering what they where and what they doing it was amazing never seen any like it


texts:
Most star systems are binary, but why is that? Why would new stars form close to others, and not (relatively) evenly spread? And even if they are clustered close together, why are the majority binary? Or are binaries the ones that survive, and systems with 3 or more stars tend to be unstable and quickly collide?

If that is so, what makes binary systems stable? Why do the stars not simply spiral in and collide, or break away shortly after creation?


texts:
I'm looking for an introductory textbook on the Magellanic Clouds, something suited for a student about to obtain their Physics BS degree (ie: not a professional astronomer).

I'm aware of The Magellanic Clouds, Westerlund (1997), but that book is:

A) Not introductory

B) 20 years old

Are there any newer and ideally more beginner friendly textbooks out there?


texts: Have auroras on Titan been observed yet?

texts:
After reading the very insightful introduction to auroras on other planets I started digging and found various questions and some answers here on the same topic, see below.
What I did not figure out yet: Have auroras been observed on the moon Titan?
I am aware that Titan does not have a significant magnetic field, but to my understanding that would only mean that the aurora would occur right at the impact point of solar winds rather than in polar regions, given that the particle flow is enough intense.
References

Comprehensive intro to Titan by phys.org
What would Aurora look like if no magnetic field was present around the Earth?
What is the science behind the polar light shapes
Why is Ganymede's aurora only visible in ultraviolet while Earth's is bright green and red?


texts: How will Starlink affect observational astronomy?

texts:
I have recently found that people around the world have been posting observations of a line of moving objects in the sky which is very likely to be a part of Starlink satellite constellation, such that there is even a meta question here about them: Do we need a notice about billionaire space ventures?.

In 2019, 19 Starlink satellites interrupted the observation of an observatory in Chile by showing up in the DECam exposure. By far, 122 satellites have been deployed, but spacex plans to launch more than 12000 satellite to complete its satellite constellation.

There have also been a few specific questions about constellations of satellites and astronomical instruments here and they reference Starlink.

However, the following question has not yet been asked point-blank: How Will Starlink Affect Observational Astronomy? Is there any citable research or science-based speculation as to the extent that Starlink will influence observational astronomy? Is it possible to address it here now?

According to Did nobody in the Astronomy community think 12,000 new satellites in LEO might be a problem? SpaceX chief operating officer Gwynne Shotwell has said

  “No one thought of this... We didn’t think of it. The astronomy community didn’t think of it.”

Now that some time has passed and people have definitely thought of it, is the likely impact on observational astronomy better understood?


texts: What stabilizes rings or accretion disks?

texts:
We think, more or less, that our Moon was formed from an accretion disk caused by a Mars-sized impactor. Cool.

Tidal forces can break apart a moon, causing rings.

Ashes to ashes, dust to dust: the moon came from an orbiting debris disk and may return to an orbiting debris disk someday.

What determines whether an accretion disk or ring system will form moons vs. remain as stable rings?


texts: How are telescopes protected from blinding light and satellite glares?

texts: I imagine a situation must happen sometimes where a telescope watching a very dark object may catch a bright flash of light or a reflection off of a satellite. If that's even a concern at all (maybe all such telescopes are already designed to exclude that possibility), what countermeasures against blinding someone's eyes or frying the digital photo sensors are there?


texts: What constraints are there on solid material in the ice giants?

texts:
Recently there has been experimental verification of superionic water ice (suggested to be called ice XVIII, not sure if this nomenclature is official yet), which turns out to be a solid (or at least, solid-ish). This has been proposed to comprise a substantial fraction of the volume of ice giant planets like Uranus and Neptune, which is something of a departure from the idea that the bulk of these planets is fluid, though potentially the presence of substances other than water may modify things.

My question is whether there are any observational constraints on the presence of solid material in Uranus and Neptune, e.g. from the gravitational moments, tidal parameters, or global oscillations ("seismology") - I'm aware that the K2 mission failed to detect any global oscillations on Neptune so I'd guess this latter method may not help much.

(There is a previous question about solids in gas giants, but that one seems to be more focused on rock rather than ice and has ended up addressing Jupiter rather than the ice giant planets.)


texts: How are image credits expressed in Astronomy presentations?

texts:
Sorry if this is a stupid question. I'm preparing an astronomy presentation, and I want to make sure I give credits where credits are due. But I see credits appear in different formats, for example:

ESA/Hubble & NASA, V. Antoniou; Acknowledgment: Judy Schmidt - a slash and an ampersand
ESA/Hubble & NASA, B. Nisini - a slash and an ampersand
NASA, ESA, and R. Humphreys (University of Minnesota), and J. Olmsted (STScI) - commas
ESA/Hubble & NASA, L. Stanghellini - commas and ampersand

If possible, I want all of the credits in my presentation to have the same format. So essentially, my question is: do a comma and a slash mean different things in image credits? Or can I write everything using the same format, e.g. for the four photos above:

ESA / Hubble / NASA / V. Antoniou / Judy Schmidt
ESA / Hubble / NASA / B. Nisini
NASA / ESA / R. Humphreys (University of Minnesota) / J. Olmsted (STScI)
ESA / Hubble / NASA / L. Stanghellini


texts: Has the Mars dust storm affected its naked-eye appearance?

texts:
Mars has been undergoing a planet-wide dust storm for a couple of months now.

By my eye, while Mars currently looks a bright and handsome orange, there's been no change that I've been able to notice from this dust storm. Is it possible for an experienced naked-eye (or small telescope) astronomer to have noticed the change in appearance brought on by this dust storm?


texts: Since we are spiraling around the black whole will we spiral into the black hole?


texts: Is it correct to assume that the relationship between an objects mass and size, is what decides if it’s a black hole or not?

texts:
I’m asking this question in reference to a scenario I saw posted a couple of days ago, where it’s stated that if you would shrink earth to the size of a cherry, it would become a black hole.

Is it also correct to assume that changing the size of earth while maintaining the mass, will not affect objects which are further away than the event horizon?

I’m asking this in reference to the same scenario as above. It is also said that changing the size of the earth, so that it becomes a black hole, will have no effect on the orbit of objects around the earth - e.g. the moon.

I’m trying to understand this, with an image of how much the earth will bend spacetime. Both as a earth-sized earth and as a cherry-sized earth.


texts: Technique for folding sparse event data in order to detect an underlying periodicity?

texts:
@JamesK's answer to When will the next transit of Earth be visible from Mars? Was the last one really on May 11, 1984? lists dates of 18 transits which I've converted to days since 1500-Jan-01 as
[35011, 44319, 73176, 109885, 138742, 148050, 176908, 213616, 242474, 251782, 280639, 317347, 326656, 346205, 355514, 384371, 421078, 430388]

Answers to Why do transits of Earth across the Sun seen from Mars follow a pattern of occurring after 26, 79 then 100 years? explain why this happens and why if they happen at all, the happen in May and November.
As an exercise I'd like to use folding to see if I can detect those or similar periodicities in addition to the 6 month periodicity.
I could

for each period of N days recalculate those modulo N
histogram the results

but since there are so few event, they rarely occur when their time comes, and so many days between events, there won't be obvious peaks in the resulting histogram.
Question: Is there a technique for folding sparse event data in order to detect an underlying periodicity?

Events convoluted with σ=1000 day gaussians purely for illustration purposes. I thought about applying some Fourier transform to this but I don't think that that makes sense, and would be cheating rather than folding.


texts: Why are the time zones calculated as 360°/24 and not 361°/24 or 360°/23.933?

texts:
Background: I'm training to be a geography teacher. Currently I have practice lessons and I'll be discussing solar time and standard time with the class. Now I stumbled over an issue to which I could not find an answer:
We teach the students:

Sidereal day: In 23 h 56 min the earth rotates 360°
Solar day: In 24 h the earth rotates 361°

We also teach that in order to construct time zones (as a replacement of solar time), one divided 360° by 24 (to have a zone for each hour of the day), which results in 24 zones with 15° each.
Now my question is: Why does one mix the measures for sidereal day and solar day? Or put differently: Why doesn't one calculate 361°/24 or 360° / 23.933?


texts: What are Trojan Asteroids and where are they located?

texts: Asides from the main Asteroid Belt, there are Trojan Asteroids - what are these and where are they located?


texts: On which side does the earth tilt to? I have tried figuring it out myself but I can't seem to find the answer.


texts: What is this planet or satellite in this picture?

texts:
I took this photo in Shijiazhuang, Hebei Province, China, 38°13'N 115°18'E
(+38.23, +115.31) on the night of February 8, 2020. Here you can see a round object above the moon, and it was moving fast,the first photo was shot on 19:32:24, and the second was shot on 19:31:46. Can you please tell me what it was? Now that I have checked on SkyView Free, it seemed to be in the location of Pollux, but I don't think it was because it was big and it seemed like a planet which did not glow.


texts: What star system/Galaxy did LIGO observe the gravity wave?

texts: Are there any coordinates for the Black Hole system, or galaxy for which the LIGO observations, observed the gravity wave? Any coordinates of the black hole system for which the gravity wave signal has been observed?


texts: What is the gain of a telescope? How would I go about calculating the gain from a flatfield image?


texts: How would the Tycho Impact have appeared from Earth?

texts:
The Tycho crater is thought to be the youngest major impact on the Moon, estimated at 108 million years ago. This puts it firmly in the reign of the dinosaurs, I find myself curious as to what our thunder-lizard brethren would have witnessed.

Roughly how bright would the initial flash have been? Would a glowing scar have been left on the Moon for days, weeks or months? Would the Earth have been subject to spectacular global meteor showers from ejected debris? Would any other effects have been felt on Earth? I'd guess that a simulation would be required to accurately answer these questions but I'm hoping that some reasonable estimates can be made by comparison of studies of other impacts.

Finally, was the Tycho impact of greater or smaller magnitude than the Shoemaker–Levy 9 impact in 1994?


texts: Is so-called Planet Nine (given it exists) observable in principle? By "observable in principle", I mean "if we knew exactly where to look, would we be able (from a technological standpoint) to get an image of the purported celestial body"?


texts: Is there any role today that would justify building a large single dish radio telescope to replace Arecibo?

texts: It seems that most of the modern radio astronomy instruments and observation that make the news are interferometers or phased array systems of one kind of another. Is there any application left for which a single huge dish is better (or cheaper) than the same collecting surface in the form of some kind of array of smaller dishes, whether relatively compact, like ALMA, or widely distributed like the Event Horizon telescope or the square kilometer array? In other words is there any point at all in considering replacing Arecibo by anything the same size?


texts: What are the best places near Kennedy Space Center to watch a night launch?

texts:
Will the below official launch viewing areas be open for a night launch (Atlas V at 7:40 p.m. on 18 Jan 2018)? If not, what are the other options?
THE LC-39 OBSERVATION GANTRY
APOLLO/SATURN V CENTER
NASA CAUSEWAY
MAIN VISITOR COMPLEX


texts: Is there a term for "path of the Sun at a given point of the Earth"

texts:
I want to buy a house and I'm asking myself what quantity of daylight the various sides of the house receive.
I know the house is roughly oriented in the east-west direction.
But I'd like to know the exact apparent path of the Sun around the house depending on seasons, with (ideally) the elevation angle of the Sun.
Is there a technical term for "the apparent path of the sun at a given point of the Earth, at a given time of the year"?
Also, is there an online tool that allows one to visualize this path on a map?


texts: How do we know so many details about Big Bang, but we do not know if Universe is finite/infinite?

texts:
I understand that this question may be too vague, but I am confused about the following:

On one hand we know a lot of "details" about Big Bang, like really precise details, evolution of universe, age of universe...

On the other hand we do not know size of Universe, or even if it is finite or not.

This seems quite weird to me, since even if we may never interact with Universe that is not observable those parts still interact with parts of our Observable Universe.

Some examples:

Age of universe: 13.787±0.020 billion years (±0.15%) determined several different ways
Hubble constant: roughly 69 to 74 km/s/Mpc (±1.6%) different measurements disagree with each other
Size of universe: unknown


texts: Align multiple fits images without WCS for future aperture photometry analysis

texts: Recently I have got a bunch of raw fits images (2048x2048 pixels) of the same sky region without WCS to process in iraf. However, those images are not well-aligned. There would be around 4~5 pixels' deviation for a specific star, thus giving me choppy batch photometry analysis result. Are there any ways to add WCS coordinate using several reference stars or create a user-defined coordinate system so that the same star would have uniform coordinates?


texts: Does the solar system also have cardinal directions? Which one is North and in what direction does it point?


texts: Is the moon moving further away from Earth and closer to the Sun? Why?

texts:
According to The NASA Moon Facts page:

  The moon is actually moving away from earth at a rate of 1.5 inches per year.

Why is the moon moving further away from the Earth? Is this a result of the moons formation that set it in motion to spiral away from us? Or is this a resultant force of the gravity from the Sun and other large bodies?


texts: How much water on the earth is made from hydrogen comes with solar wind?

texts: A great fraction of solar wind is protons or Hydrogen ions. Some part of it is captured by Earth. I am wondering how much water in my half a liter cup is made of hydrogen from the Sun.


texts: Or would the planet(s) need to be too far away for life to exist?


texts: Who first used two lambdas to typeset the wavelengths of a spectra line doublet?

texts: Also what is the accepted or most common way to typeset the wavelengths of a doublet? e.g. lambdalambda-3727,3729 with or without a hyphen? and without the Angstrom symbol?


texts: What exactly are the "ν6 secular Sun-Jupiter-Saturn" and the "1:4 Sun-Jupiter" resonances?

texts:
In the recent Acta Astronautica article The edge of space: Revisiting the Karman Line, Harvard-Smithsonian Center for Astrophysics astronomer, Space SE contributor and "inverse namesake" of asteroid (4589) McDowell Johnathan C. McDowell lists a number of different boundaries in the solar system in section 3.2. One of them is described as the following:

  The ν6 secular Sun-Jupiter-Saturn resonance which marks the conventional inner edge of the asteroid belt at 2.06 astronomical units (308 million km) from the Sun (26); it coincides with the 1:4 Sun-Jupiter resonance (27) and asteroid orbits near this resonance are unstable, soon perturbed to enter the inner solar system. Although there is no generally agreed definition, this location is a reasonable place to mark as the boundary between the inner and outer solar system.

What (the heck) are the ν6 secular Sun-Jupiter-Saturn and the 1:4 Sun-Jupiter resonances exactly?


texts: Why does half of a planet's radius end up being the radius of the core?

texts: This answer makes the assumption that the ratio between the radius of a planet and the radius of its core is roughly constant shortly after planetary formation. Why should this be the case? Do we know why, when a planet forms, it ends up with half of its radius being core?


texts: Where is the materials of comet after it crashed into the sun?

texts: If a comet crashes into the sun, where will the substance (eg: water,silicon) be? Will they be inside the sun? Or they will be ejected from sun again?


texts: Where can I find detail on interpreting the exo-planet transit-data graphics used in the Zooniverse Project?

texts:
I'm participating in the Zooniverse Exoplanet-explorers project (transit method), which provides only minimal guidance on interpreting their light curve and transit data graphics, as visible here:
 https://www.zooniverse.org/projects/ianc2/exoplanet-explorers/classify

Can anyone point me to source(s) that will help me read these graphs in detail, pls?

(Re own comment below, suggest view Weird example)

UPDATE: Just located NASA Exo-PLanet Archive which looks like it might hold what iSeek. But further recommendations would be appreciated.


texts: Which celestial body is able to come closest to Pluto?

texts: Other than Pluto's moons (including Charon), which known body comes closest to Pluto, and how close? Neptune doesn't come closer than 16 au. What about Orcus, whose orbit is similar to Pluto's, or another dwarf planet?


texts: What is the relationship between the focal length and f number of a telescope compared to a guide scope?

texts:
How do you determine the optimal length of a guide scope for a given imaging telescope?

I imagine it would have to take into consideration the pixel size of the guide scope, but would the aperture matter as well?


texts: Do all stars have the potential to have life supporting planets?

texts: Regardless of how big or small, how hot or cold, do all stars have a goldilocks zone, and if so, could any given planet in this zone (with the right configuration) support life?


texts: Can a Thorne-Żytkow object be the progenitor of a modern quasi-star?

texts:
I was reading some Wikipedia articles about astronomy, and came across an interesting line:

The neutron star may also accrete sufficient material to collapse into a black hole.

Now, here is my theory:
If a massive supergiant star ($>20 M_\odot$) has a neutron star at its core, eventually the neutron star will pass the TOV limit, collapsing into a black hole. So if the new black hole is still in the star's core, and the outer envelope is not ejected, will a modern quasi-star be formed? If so, how long would it live for?


texts: Can life survive on the equator of cooled and fast rotating white dwarf or neutron star?

texts:
As I know, some stars produces carbon, nitrogen and oxygen when they are old and become white dwarfs or neutron stars. And even their surface gravity is strong, it may rotate very fast so that the surface gravity is diminished, hence materials such as rocks and water can present at the surface normally.

My question is, is it possible for life (eg:bacteria) to survive on the equator of white dwarf or neutron star if it is cooled and rotate very fast? Or is it even possible for the equator of white dwarfs or neutron stars become the origin of life?


texts: plotting stars in cartessian coordinates using the stars ra and dec produces the wrong location of the stars

texts:
I am currently running into some problems with plotting some stars locations in a Cartesian coordinate system.
The stars aren't in the right order and I'm not sure where I am going wrong.

I first use the equation (where S is a vector)

S = [cos(ra)*cos(dec), sin(ra)*cos(dec), sin(dec)]

to obtain a vector S of the star.
I now want to obtain the x and y positions of the stars In terms of a 2d coordinate system so I use

c * sx = S * px / S* pz
c * sy = S * py / S* pz

where C is the scale ratio of pixels to tangent of the angle of the camera and P is the vector center of the camera.(Im using this because I'm trying to find the distance between each pair of stars when a photo of the stars is taken by a camera)

px = unit vector X
py = unit vector Y
pz = unit vector Z

and I solve for sx and sy. When I plot the stars location with sx and sy however I do not get the right locations of the stars. Any guidance?


texts: Why don't globular clusters flatten with a galactic disc?

texts:
Globular clusters lie in the galactic halo, outside of the disc. However, galaxies are more or less a collection of material and objects — why is it, then, that most stars form a plane due to the angular momentum, but some patches of stars do not?

In fact, globular clusters often contain some of the earliest stars formed in a galaxy, right? How come they do not flatten, yet a lot of the older stars do?


texts: Can I take logarithms of magnitudes (which are already log)

texts:
I'm investigating the relationship between the magnitude of quasars in various wavelengths, and their redshift $z$. I've found that if I take the $log$-$mod$-transform ($L_{mag}$) of the magnitudes, where

$L(y) = sgn(y) * log(|y| + 1)$

which I got from here and here, I can get a slightly tighter fit for my data, which is the aim of the study. Here's a plot for the W1 magnitude and $L(W1)$ as above, both against $log(z)$:

showing the regression coefficient for each.

My question, before I take this to my supervisor, is: is there any reason why I shouldn't be taking the $log$ of an already $log$ quantity?


texts: Could the big bang have created super massive black holes?

texts:
I understand that space was compressed to a single point and that during the big bang all points within that expanded away from each other at phenomenal speeds. I also have heard that during this the universe wasn't the same everywhere, as in small quantum fluctuations that expanded to macroscopic scales.

Would this mean that higher density than normal areas could create massive black holes? Maybe not as big as the ones today but perhaps large enough to solve some of the problems with super massive black holes being observed in a short amount of time after the big bang

I am not asking "why didn't the universe turn into a singularity?" I am asking "Could the variable density afterwards create many singularities which could explain for the problems associated with super massive blackholes?".


texts: What happens to the Fourier Transform of the Measured Spectrum?

texts: What happens when you double the width of the entrance slit of a spectrograph, in turn letting in twice as much light, would there be an improvement in the Fourier transform of the measured spectral profile d(f) following to higher frequency f?


texts: Formulae for gravitatitional equilibrium

texts:
I am trying to calculate at which point gravitational equilibrium sets in for various bodies (planets stars neutron stars etc.) assuming they are perfect spheres. However, the radius I get is not equal to what it should be according to Wikipedia (I tried it for the Sun, a planet and a neutron star, but all of them were off by quite a bit).

Below is the example of the neutron star radius I'm trying to get:

My result (factor) is 1 at:

Radius: $2228588\mathrm{\ m}$

Density: $1.2768744892680034 \times 10^{11} \mathrm{\ kg/m^3}$

The Wikipedia article about neutron stars says the radius of a neutron star is about 12 km and the density is about 10 times higher than mine. My result is 2228km, which is quite a bit off, so I have a second question:

Am I calculating all the forces I need?
Are the formulae I'm using correct?

I took them from Wikipedia and university slides and I found multiple variations of almost all of them (most of which I actually didn't list below), so I'm quite confused as to what is correct.

I know that I'm using iron as the element and I should split it up and convert the protons to neutrons, but that would only increase the degeneracy pressure and result in an even bigger radius, if I'm not mistaken.

Here's how I calculated it:

Mass of an electron: $M_e$

Standard atomic weight of hydrogen: $M_h = 1.00782503223$

Mass of a neutron: $M_n$

Atomic mass of ${\mathrm{Fe}^{56}_{26}}$: $55.934936 \mathrm{\ u}$

Number of atoms: $7.938 \times 10^{31}$

Number of neutrons per atom: $(56-26) \times \text{number of atoms}$

Number of electrons per atom: $26 \times \text{number of atoms}$

Total number of particles: $\text{number of atoms} + \text{number of electrons}$

Mass: $\text{atomic mass} \times \text{number of atoms} = 4.4400513610370694 \times 10^{30} \mathrm{\ kg} \approx 2.3M_☉$

Radius: $2,228,588 \mathrm{\ m}$

Temperature: $9.452 \times 10^{-7}° K$

Force of gravity: $\frac{GM^2}{r}$

Volume: $\frac{4\pi r^3}{3}$

Particle density: $\frac{\text{number of particles}}{\text{volume}}$

a: $\frac{4\sigma}{c}$

Radiation pressure: $\frac{a T^4}{3}$

Gas pressure: $\text{particle density} \times k_B T$

Electron degeneracy pressure: $\frac{\pi^3 \hbar^2} {15 M_e} \times \frac{3 \times \text{number of electrons}} {V \pi}^{\frac{5}{3}}$

Electron degeneracy pressure 2: $\frac{\pi^2 \hbar^2} {5 M_e \times M_h^{\frac{5}{3}}} \times \frac{3}{\pi}^{\frac{2}{3}} \times \frac{\frac{M}{V}}{1}^ {\frac{5}{3}}$

Neutron degeneracy pressure: $\frac{\pi^3 \hbar^2 }{15 M_e} \times \frac{3 \times \text{number of neutrons}}{V \pi}^{\frac{5}{3}}$

Neutron degeneracy pressure 2: $\frac{3^{\frac{10}{3}} \hbar^2 }{ 15 \pi^{\frac{1}{3}} \times M_n^{\frac{8}{3}} \times r^5} \times \frac{M}{4}^{\frac{5} {3}}$

Total pressure: $\text{gas pressure + radiation pressure + neutron degeneracy pressure + electron degeneracy pressure}$

Total pressure force: $\text{total pressure} \times \text{volume}$

If total pressure force = force of gravity, then the body is in equilibrium.


texts: Satellites traveling in single file across the sky

texts: I just watched 46 (best count) satellites traveling in single file, about 3 second intervals between them. Is that possible?  I don't want to believe they were UFO's.  Time was 06:20 ET


texts: How do I find the signs that planets are in during any given date?

texts: Say for example I wanted to know where the planets were on December 19th, 1664, at 1am; how do I figure that out?


texts: A vertical stick's shadow at solar noon should be straight north/south, right?

texts:
At true solar noon, the subsolar point should be directly north or south of you, and therefore a vertical stick's shadow should point directly north or south, right?

The Wikipedia page for Sun Path is confusing me.  It claims that at the equinoxes, a vertical stick's shadow will point 23.5° off of true north or south.  It says that you only get straight north/south shadows at solar noon at the solstices.

  On the equator, the sun will be straight overhead and a vertical stick will cast no shadow at solar noon on the equinoxes. On the vernal equinox, north of the subsolar point (on the equator) the vertical stick's shadow will point a little westwards of true north (NNW) reading 336.5° from true north and little eastwards of true south (SSE) reading 156.5° from true north. On the autumnal equinox, north of the subsolar point (on the equator), the shadow will point a little eastwards of true north (NNE) reading 23.5° from true north (and south of the subsolar, the shadow will point a little westward of true south (SSW) reading 203.5° from true north).

  --https://en.wikipedia.org/wiki/Sun_path#Shadow_of_a_vertical_stick_at_solar_noon

Why would this be true?  My understanding is that true solar noon is defined by when the Sun is directly north or south, and the subsolar point is on your longitude.  Mean solar noon is a different story, thanks to the equation of time.


texts: What would happen if space-time began to contract?

texts:
Assume that the expansion of the universe stops and it starts to contract again. What would happen?

Would only distances between objects get smaller, or are there other effects we can expect?


texts: Can we detect pulsars that aren't "pointed" towards us?

texts:
A pulsar is a highly magnetized rotating neutron star that emits beams of radiation through its magnetic poles, in the direction of the Earth. This makes it seem to pulse, as seen from Earth. There likely are similar objects that pulse as seen from other directions, but not from Earth. Can we tell the difference between one of these objects and an ordinary neutron star?

Is there any way of detecting pulsars that are not pulsing in our direction?


texts: Probability of collision of another bubble universe with our universe

texts:
This is rephrased from a previous question and expanding on it. Considering the model of an "inflating" universe which extends infinitely in past (and possibly future) time, constantly creating new space within itself: within that inflating universe, at any point with some low probability per unit of time, a phase transition (like water freezing to ice) can start to happen, fundamentally changing the nature of space and time at one point. That effect propagates out (again like supercooled water freezing) creating a growing bubble of this changed space-time, which in an abuse of language, we call "a bubble universe".

Assuming the rate of expansion during inflation is known (rate of expansion of 10^26 every 10^-32 second to achieve a flat universe), the size of our visible universe is known (17Gly), is it possible to calculate the unit probability per unit of time a phase transition occurs during inflation that would be necessary for another universe to collide with ours with likelihood 95%. If we hypothesize that the inflation field is a scalar field of known value consistent with quantum field theory, would this probability of transition be consistent with quantum fluctuation in that field?


texts: What is $\omega$ and $\tau$ in this celestial sphere

texts:
In the celestial sphere below, what is the $\omega$ and $\tau$ physically? I mean, In the normal world, how do we see them? for example, we can see the altitude of the sun (a) by examining the shadow of a pillar and comparing it with its height, How do we see $\omega$ and $\tau$ in real world?

S is the sun and W is the west.

Also  I want to know how do they effect on the shadow of wall which is built in direction of "$SCP$ to $NCP$".


texts: Is there online data on asteroid axial tilts?

texts:
I am hoping to find axial tilts for asteroids and also their spring and fall equinox. Some of the asteroids I'm interested in are:
4 Vesta, 1 Ceres, 24 Themis, 65 Cybele, 153 Hilda, 624 Hektor


texts: Light that travels eternally because of inflation?

texts:
What happens with electromagentic waves that are emitted into
intergalactic space, but reach not any object because of inflation? Lets assume that photon A and photon B are emitted. Photon B hits some object, photon A enters a gigantic void or simply has nothing in its path, and heads for the horizon, so to say.

Relativity tells that A and B do not "feel" time passing. From our point of view B travels a finite time, while in the frame of B the object is reached instantly. However, since A will be eternally underway, what is going to happen? We have kind of a zero*infinity travelling time in the frame of A.

Do our models make statements about this? Or is there some explanation


texts: How to calculate the flux of a galaxy merger?

texts: Say three galaxies, with equal fluxes, $f_1$, merge. How could I calculate their combined flux?


texts: How do we know about the origin of ʻOumuamua?

texts: How do we know that ʻOumuamua is interstellar and not otherwise? I fail to understand the logic that the extraordinary speed of the object proves it to be of interstellar origin, and that our sun's gravity failed to capture it.


texts:
After a couple months of watching a very bright Venus appear at dusk and set soon after the Sun, I've noticed that it seems to have temporarily disappeared to the naked eye. I used a virtual sky simulator (Stellarium) to confirm that the Evening Star has indeed transitioned to being the Morning Star (though due to obstacles blocking my view of the horizon in my backyard, Venus is still too close to the Sun for me to witness it at dawn before sunrise renders it invisible).

What is the period of Venus's alternation between morning and evening visibility? I gather this isn't a simple seasonal period as its visibility should depend on the Sun-Earth-Venus angle rather than just Earth's yearly orbit.


texts: Questions about terminology used for Mars and its moons

texts:
I am having difficulty with some terminology:

sub-Martian hemisphere of Deimos ... what place on Deimos does it refer to?
leading/trailing apex of Phobos ... what place are those?
Apex ... in general it means a top of something, or an end of something pointed; but what does it mean on a relatively spherical body?
Anti-Mars meridian ... is this a meridian on the side of the moon facing away from Mars?

Thank you.


texts: Star - Black Hole binary. Star core Collapses. Does the black hole immediately grow from neutrinos?

texts:
I was reading on how Type II Supernovae release as much as 99% of their energy as neutrinos. So I was thinking: suppose there was a large star and black hole binary system, but the two were not close enough for the BH to draw mass out of the star, so the star aged naturally instead.

If one were close enough to observe when the star's core collapses - but before the supernova bursts through the star's surface - would it be possible to see the black hole immediately grow in size for no apparent reason as it eats up the neutrinos from the companion star's collapse?


texts: What could a cloud of mini radio dishes see?

texts:
Suppose an astronomer gave a 1 m radio dish to 500 people scattered over the face of the Earth and connected them to the internet. The people are directed to set their radio antennae up in their backyard per given instructions. The astronomer would then control the array of radio antennae remotely via the internet.
Could such an array of radio dishes be used to do any kind of meaningful astronomical interferometry? If so, what kind? If not, why not?
I fully expect that the radio dishes wouldn’t hold a candle to the sensitivity other radio dish networks (EVT, VLA, EVLA, etc.) due to the tiny dish size. I expect time synchronization would be an issue, but perhaps they could find a clever way to synchronize. I imagine this array would have very high resolution due to the large number of large and small baselines — extended further by the Earth’s rotation. Between low dish sensitivity, large numbers of dishes and a huge baseline count, I’m curious what such a network could be capable of.


texts: Do higher-metallicity elliptical galaxies, that formed rapidly, have a larger velocity dispersion (lowercase-sigma)?

texts:
https://academic.oup.com/mnras/article/445/3/3092/1036122?login=true
And, .....
https://www.newscientist.com/article/mg24933160-200-how-every-galaxy-comes-from-quantum-fluctuations-billions-of-years-ago/
Sorry, in advance, for my poor understanding, but do higher metallicity elliptical galaxies have faster stars and a higher velocity dispersion (lowercase-sigma and sigma-squared)?
And, elliptical galaxies that formed more rapidly, with most or all stars of a similar, older age, also have a higher velocity distribution?  With, therefore more high-speed stars?


texts: What's the proper terminology for nebula clouds?

texts: I'm writing a research paper over outer space (yeah, yeah, broad topic) and I'm wondering what the proper terminology for nebula clouds is.  This is an excerpt from my paper showing how I'm going to use the term:  "Outer space is the host of all the types of stars and galaxies and a lot of other interesting phenomena, such as black holes, supernovas, and ________."  Long story short, would I use "nebula clouds" or "nebulae"?


texts: How is the distance of a star from Earth calculated in the HYG star database

texts:
The HYG star database can be found here

From the hygdata_v3.csv file, how are the cartesian (x,y,z) coordinates calculated? (Is there a mathematical formula for this?)

And in the dso.csv file, there aren't any x,y,z coordinated. How can I calculate that?


texts: What is causing this strange shimmering pattern of light during a total solar eclipse?

texts:
Below this question was left a comment linking to the Smarter Every Day video Space Station Transiting 2017 ECLIPSE, My Brain Stopped Working - Smarter Every Day 175.

At about 04:30 they show a short clip of a video recording of what looks like a white bed sheet hanging vertically and a shimmering pattern of light on it, I assume related to the total solar eclipse.

What's going on? What causes this? What's it called?


texts: Given a collection of pixels, how to deduce the flux from them?

texts: I've obtained the coordinates of brightest pixels from different images (.fits files) using Python. I want to get the flux of each pixel. How do I go about finding out the flux?


texts: Why does the Moon never set in Svalbard, Norway?

texts: I heard in a documentary that, in Svalbard (Spitsberg), Norwegian archipelago in the Arctic Ocean, the Moon never sets. Why? A drawing would certainly help.


texts: How is accurate spectral analysis of a planets atmosphere achieved, bearing in mind that its host star's resultant light emission is not a full spectrum?


texts: Distance between objective lens and eyepiece

texts: I am trying to make home telescope, I have a convex lens of focal length 1000mm and eyepiece (plano-convex) with 25mm focal length. What is the ideal distance between objective and eyepiece to see objects more than one kilometre away.


texts:
(1) Please go through following image
Possible Super Red Giant?
However sdss shows it as galaxy! Am I missing something.

(2) Google Sky shows object in latitude and logitude format like this.
Is there any way to convert those numbers to Right Ascension (ra) and Declination (dec) numbers or opposite of that  so that I can spot google sky data on SDSS and SDSS object on Google Sky?


texts: If the space is expanding near the speed of light or the speed of light, why Andromeda is approaching or coming near to our galaxy (Milky way)?

texts: Space with distance of 1megaparsec is expanding with rate of 70km/s, and if space with a distance of 4296 megaparsec is expanding at rate of 300,720km/s, then why Andromeda is coming to us? Even there has a dark energy that accelerate the space expansion? Why?


texts: Is our central black hole actually at the CG of the galaxy?

texts:
It seems fairly certain there is a large black hole, about 25,000 ly from Earth roughly in the center of our galaxy, in the direction of the Sag. A radio source.

• In fact, is it thought to be literally at the center of gravity of our galaxy?

Does we know, or is this uncertain?

• Indeed, do we actually know where the CG of the galaxy is?

I observe that the term "Galactic Center" seems to be an astronomical term. (Example.) Can an astronomer tell me: does that term mean what we believe to be the CG, or rather, is it a nominal mapping point?

• If the black hole IS exactly at the CG of the galaxy ... why?

It would seem to me a big BH could form any old place, and perhaps still be orbiting or oscillating the CG - right?  If the SBH is literally the CG of there galaxy, is there a reason for that?  (Like, "SBH can only form at the CG" .. or "stellar collisions can only happen at the CG" .. or whatever, those are only wild guesses.)

Or indeed, is the SBH the "main player" in the galaxy - just as the solar system formed around the sun (so it would be silly to ask "why is the sun at the center"), did the SBH sort of co-form with the galaxy (or something?)

In any event, is the SBH at the actual CG of our galaxy? Do we know?


texts: Was the progress of astronomy in the 1800s surprisingly slow, and if so why?

texts:
The 1800's was a century of fantastic scientific discoveries in chemistry, geology, biology, engineering and so on.  Is it correct to say that astronomy did not keep up with this development? And if so, why? If not, what might be some main reasons for me (and others) having this impression?

The late 1700's saw a couple of revolutions in astronomy such as the discovery of Uranus as the first non-antique planet and the measurement of solar system distances thanks to the transits of Venus. As I understand it, the next big leaps in astronomy came in the early 1900's with the HR-diagram and the "discovery" of galaxies and more. The view of the universe did not seem to change much between 1800 and 1900. Nowadays every decade has its revolution such as inflation, dark matter, dark energy, exoplanets.

Spectroscopy, optics, photography, Doppler effect, and electricity all developed greatly during the 1800's but don't seem to have brought any revolution to astronomy until later. Is relativity and quantum physics behind this new flourishing? Had the Newtonian physics reached its limit for potentially revolutionizing astronomy already about year 1800? Or was astronomy just out of fashion, maybe because of more profitable employment for the brightest brains in the age of industrialization?


texts: two black holes orbiting each other within their event horizon

texts:
Is there any argument against this situation: two black holes, one within the event horizon of the other, and the system is stable.

It is interesting to me because that if this works, we could have the system's event horizon not in the shape of a perfect sphere. (The event horizon would probably be moving with the orbit)


texts: How do observational astronomers manage streaks and other artifacts from objects in Earth Orbit?

texts:
There are thousands of satellites and spent rocket parts in low earth orbit (LEO). Mostly near the lines of dawn and dusk they can be in sunlight while observatories below are still viewing the night sky, as are the observatories like Hubble (also in LEO).

They are moving roughly 7 km/sec and as seen from Earth that motion will be roughly a half-degree per second, depending on distance.

Considering the number of observatories imaging the sky at any moment and the number of objects in LEO, streaks across images must be happening quite regularly.

While that would strongly impact a one-hour exposure on emulsion, these days solid state imaging is used and these are probably regularly buffered to provide the dynamic range necessary to capture dim objects with very bright images in the same field.

While a fraction of a second streak by a satellite will not normally completely obliterate a long exposure, it is still a problem and it seems would have to be managed in an accepted and systematic way.

Question: How do observational astronomers manage streaks and other artifacts from objects in LEO? Since these things are (usually) carefully tracked and their trajectories predictable, do observatories, or at least observers, ever plan ahead for these events, or schedule to avoid them? Or is it just handled automatically in post-processing?

For subtext, see astronomer Alex Parker's Tweet (image shown below) and then astronomer Benjamin Pope's more recent Tweet about the Humanity Star, as well as his response "Oh god why would you do this to us astronomers"? response here.

Also see:

The Washington Post: Company shoots shiny orb into orbit and angers astronomers over ‘space graffiti.’
New York Times: Is This Shiny Satellite Sky Art or ‘Space Graffiti’?
Scientific American: Twinkle, Twinkle, Satellite Vermin

Within Stack Exchange:

How will several thousand Low Earth Orbit satellites affect the night sky?
What is the name of the polyhedral shape of the Humanity Star?
Does Humanity Star have non-reflective triangular panels? If so, what are their characteristics?
Two week mark; has Mayak (Маяк) been spotted yet? Reflector deployed? Astronomy “ruined”?

From Alex Parker's Tweet:


texts: What is the present day radius of the observable universe?

texts:
The radius of the observable universe is generally taken to be ~45 billion light  years. However, we see distant galaxies as they were many millions of years in the past, so there are two ways I can interpret this radius value:

1) Light that is reaching Earth for the first time today was emitted by ancient galaxies that were initially a lot closer, but are now estimated to be 45 billion light years away from us.

2) Light that is reaching Earth for the first time today was emitted by ancient galaxies that were initially 45 billion light years away, and are now a lot further.

Which interpretation, if they're not both wrong, is correct?


texts: Why can't different regions of the universe be the same as they have the same origin?

texts:
The horizon problem states that because of the speed of information can't be faster than light and the distances between far regions are too big there is a problem because they look quite the same. Therefor, the inflation is introduced.
But what I don't understand is why those regions can't be the same without inflation or something like that? They have the same origin and the universe was in the beginning too empty to make a difference for the direction you went. So in my simple understanding, it is rather expected that they should be the same but why are cosmologists think different about that?


texts: Why don't we have a browsable spacetime augmented virtual solar system?

texts:
Wouldn't it be nice to be able to render any viewpoint from all the data transformed into a point cloud, an augmented virtual reality of moving objects in our solar system.

I would just like to be able to chose any point in the solar system and view exactly what is there at a specific time.

It's possible to extrapolate 3D data from multiple viewpoints of an object, don't we have enough satellite data to do it?


texts: What is the horizontal distance needed to observe an object just as badly as if it where in space at the zenith?

texts:
When I see an object in space (let's say the ISS) above my head, my line of sight traverses ~$100\; km$ of atmosphere. The vast majority of the extinction, absorption and turbulence happens closer to the surface of Earth (since the density of air follows an exponential decay with altitude).

If I tried to observe another object, this time on the surface of Earth, the line of sight towards it would have to traverse huge amounts of air and the density would in principle be constant throughout the entire optical path.

My question is: How should I calculate the maximum distance of an object on the surface of Earth such that the image I can get from it is still better than the image I can get for any object outside the atmosphere in the zenith of an observer located on the surface of Earth? What is the distance for an object on the surface of Earth at which anything I photograph in space looks crispier than this object?


texts: How quickly does a supernova heat up/expand?

texts:
Suppose there's a star out there that's a lot more massive than the Sun.

Suppose further that orbiting this star is a planet not unlike Earth. Water, oxygen, civilization, and all.

Now the star decides to go supernova. How quick, or slow, is the process?

How long will it take it to heat up to make life on that planet impossible? A month? A year? A hundred years? A thousand years?

And how long will it take for the supernova to engulf the planet? A day? A month? A year? A million years?